Process for the perforation of billets



Dec. 17, 1963 H. FRANK 3,1 14,203 PROCESS FOR THE PERFORATION 0F BILLETS Filed Dec. 1, 1959 7 F/g. I 5

Myen/or Han/75 Fran/r By Ms af/omeys United States Patent PRGCESS FGR THE PERFDRA'HON 0F BILLETS Harms Frank, Witten (Ruhr), Germany, assignor to Mannesmann Aktiengesellschaft, Dusseldorf, Germany,

a company of Germany Filed Dec. 1, 1959, Ser. No. 856,533 Claims priority, application Germany Dec. 3, 1958 1 Claim. ((11. 29-534) This invention relates to a method for piercing a solid billet of metallic material which can be deformed only with difiiculty, such materials being defined as those in the group consisting of molybdenum, titanium, zirconium, tantalum, alloys thereof with nickel, chromium, and the like, or steel having a high content of chromium, nickel, molybdenum, and the like. The method involves a heated billet being set in a holder and then pierced by a mandrel or punch. The method can be used for a formation of a hollow billet which can then be further processed in any desired manner. For example, by extrusion pressing the hollow billet resulting from the new method can be used for the production of tubes.

In conventional procedures for piercing billets of metals of the group above mentioned, experience has shown that driving of the mandrel into the heated billet, even when a lubricant is used, very often results in defects on the inner surface of the hollow billet. Such defects, for instance, may be transverse cracks which are dificult to control. They may be due to the cooling effect of the piercing mandrel, to the heat sensitivity of the material, to local temperature variations inside the billet, to the properties and effects of the lubricant, to the rate of deformation, or to many other variables. Such defects are usually magnified during the further processing of the hollow billet when it is elongated into a tube. This causes considerable loss of time and material. It is not possible to produce perfect tubing from materials such as those mentioned in the above group in a combined piercing and extrusion process which is continuous except with the production of a considerable amount of scrap material.

The principal object of the invention is to provide a method of obtaining a defect-free inner surface on a hollow billet so that the end product produced from the billet as, for example, a tube, can be used immediately without having to machine the inner surface. It is characteristic of the method according to this invention that a heated disk is placed upon the heated billet, the disk being immovably connected to the billet by means of welding, prior to the piercing step, the heated disk being made of a metal which has a melting point above the temperature to which the billet is heated. The disk has a thickness of less than half the height of the billet and a mass suflicient to coat the entire inner wall of the hole produced by the mandrel in the billet. The material of this disk is also more plastic at said temperature than the metal of the billet. The heating of the disk and billet can be done simultaneously or separately as desired. When the disk has een properly positioned, the piercing mandrel is forced through the disk and into the billet by punching out some of the material in the disk with the result that a lining of the metal of the disk is formed on the walls of the cavity pierced in the billet. These inner walls formed by the piercing mandrel may extend part way or all the way through the billet. In this description where piercing is spoken of, it may refer to either a cavity which goes only part way through the billet, or a perforation which goes all the way through.

In the drawings there is shown schematically an example of how the invention can be carried out.

FIG. 1 is a view in section through a press with a 3,ll4,23 Ce Patented Dec. 17, 1953 solid billet and a disk in the holder, the piercing mandrel being ready to begin its descent into the billet.

FIG. 2 has a similar view showing the parts after the mandrel has deformed the disk and billet with the smooth inner wall of the hole formed of the disk metal.

Referring to these drawings, the press comprises a holder 1 with an extrusion press die 2 near the bottom of the holder, having an opening therein for the end of the piercing mandrel. A billet 3 is shown in the holder resting upon the die 2. As already mentioned, the billet may be formed of molybdenum, titanium, zirconium and tantalum, either by themselves or in combination with one another or in an alloy that contains these metals. Furthermore, the group of materials of which the billet may be formed includes steel and in particular an austeni'tic steel. The steel may contain chromium, nickel, molybdenum, tungsten or vanadium either singly or in combination with one another.

For a specific example of a billet suitable for this method, reference is made to a billet made of steel containing 0.4% of C, 19% of Cr, 13% of Ni, 10% of Co, 2% of M0, 2.5% ofW and 3% of Nb.

On top of the billet 3 is a disk 4- which may, for example, consist of iron or steel unalloyed or containing chromium, nickel, molybdenum, tungsten, vanadium, singly, or in combination. It is an advantage to use a metal which may be welded to the billet. For this purpose the disk may be joined fixedly to the billet, for example, by a peripheral seam 5 done prior to the heating of the disk so that the billet and the disk are heated together. With the specific example of billet metal given above, it is found that a disk of soft unalloyed steel produces a perfect result.

The term disk is used throughout the specification and claim to designate a structure which has considerably less thickness than the billet to be pierced. Preferably the thickness of the disk is less than half the height of the billet. The lower limit of the disk thickness may be defined as follows:

The mandrel entering the disk shears out a part thereof and carries said portion as a plug into the billet to be pierced. This causes the metal of the plug to flow slowly over the leading edge of the mandrel and along the mandrel and is deposited as a firmly adherent lining or layer on the wall of the formed cavity. This lining or layer forms a protective layer which, during the piercing operation, prevents injury to the inner face of the billet and which participates in the deformation of the billet on its extension. It is of no importance whether the tube is drawn immediately after piercing, or whether this is done later independently of the piercing step. From the foregoing, it will be readily understood that the relation of thickness of the disk to height of the billet must be so chosen that the wall of the cavity or aperture produced in the billet must be completely covered by a layer of the disk metal.

The diameter of the disk will be preferably the same as that of the billet.

Above the holder 1 is a piercing mandrel 6 with a ram 7 around it. Prior to pushing mandrel 6 through the heated combination billet-disk 3, 4, the ram 7 is lowered into the upper end of the holder 1 so as to close the same. In the following piercing step, the mandrel shears a plug out of the disk 4 and pushes said plug through the billet 3. On this passage the material of the plug is distributed between the periphery of the mandrel and the corresponding inner wall of the produced cavity of the billet.

The obtained pierced billets may be, of course, extended to tubes by other methods than through extrusion presses. The novel method may be used for the manufacture of plated tubes, as well as for obtaining linings in tubes which are processed by cold drawing methods such as in cold Pilger tube-reducing or plug drawing installations.

What is claimed is: A process for the production of a defect-free bore of a hollow block made from an initially solid billet of austenitic steel having a high content of chrome, nickel, molybdenum, tungsten or vanadium comprising the steps of peripheral seam welding to that end face of the billet which is turned toward the piercing mandrel a mild steel disk having a diameter preferably equal to that of the billet and a thickness less than half that of the billet, heating the billet and disk to Working temperature, and piercing the composite billet to hollow the same References Cited in the file of this patent UNITED STATES PATENTS Wheeler June 1, 1943 Bardgett May 30, 1961 FOREIGN PATENTS Great Britain June 18, 194-8 Great Britain Feb. 1, 1956 

